The present invention relates to a method and a device for recognizing rotational speed fluctuations/rotational torque fluctuations in a drive device, in particular in a motor vehicle wherein this drive device has at least one combustion engine and at least one torsional vibration influencing device, in particular a dual mass flywheel. In the following the method according to the invention is explained by way of a motor vehicle with combustion engine, it is noted that such a method can also be used in hybrid vehicles and vehicles with range extender.
Usually combustion engines are used in motor vehicles which work according to a discontinuous combustion principle, in particular, these are two stroke or four stroke combustion engines, which depending on the utilized fuel are mostly referred to as Otto or Diesel engines. Based on their working principle, these combustion engines have in common that a generated rotational torque is discontinuous and is subject to certain fluctuations. Such fluctuations occur independent of the kinematic of the combustion engine, in particular independent of whether the combustion engine is constructed as a rotary piston engine or as reciprocating engine. These rotational torque fluctuations oftentimes result in undesired rotational torque fluctuations in a drivetrain of a motor vehicle. Such rotational torque fluctuations usually cause additional stress for the drive train and are mostly perceived as bothersome by vehicle occupants, therefore many motor vehicles have devices for influencing in particular for reducing these fluctuations. Devices that have proven to be particularly effective for reducing interfering torque/rotational speed fluctuations are so called dual mass flywheels. In particular dual mass flywheels but also other devices of a drive device often have an natural vibration behavior (natural frequencies). When these devices are excited in the range of the natural frequency with vibrations this can lead to an unfavorable operating behavior, this results in the fact that these devices have operating ranges to be favored, operating ranges to be less favored and operating ranges to be avoided. Operating ranges to be avoided are in particular those within which the corresponding device is excited to vibrate with its natural frequency (resonance). In this regard it is usually very important for the operating range of these devices with which rotational speed/torque fluctuation or respectively with which sequence of rotational speed/torque fluctuations these devices are impinged. In order to be able to take the rotational speed/torque fluctuations into account when controlling the drive device it is important to first sufficiently detect the same.
From the state of the art methods are known by means of which rotational speed/torque fluctuations can be detected. From WO2010/121888 it is known to determine a local maximal value of the rotational speed, to determine the differential value between this maximal value and the actual rotational speed and to turn off the combustion engine in dependence on this differential value.